Lubricants and extreme pressure additives therefor



Patented Feb. 28, 1950.

LUBRICANTS AND EXTREME PRESSURE ADDITIVES THEREFOR Elmer B. Cyphers, Cranford, N. J., and Louis J. Osborne, Jr., Brooklyn, N. Y., assignors to Standard Oil Develop ration of Delaware No Drawing. Application November Serial No. 708,794

ment Company, a corpo- Claims. (0!. 252-463;)

The present invention relates to lubricants and extreme pressure additives therefor. It pertains more particularly to lubricants of the general type mentioned above, wherein materials such as phosphorus and sulfur, and compounds thereof, are included in mineral and/or fatty oil bases to form high pressure lubricating compositions.

In many types of modern machinery, very high unit pressures occur between the adjoining parts of moving metallic surfaces, Unless such surfaces are effectively and continuously lubricated, rapid wear and early destruction occur. At the pressures which are sometimes employed, particularly when operating at high speeds or high torques and high temperatures, conditions arise under which ordinary lubricants are not capable of maintaining protecting lubricating films. In such cases the lubricating films of oil are commonly supplemented or replaced by thin layers of chemical compounds which are formed on and from the metal of the cooperating machine parts. Thus, as is well known in the art, certain substances, such as sulfur, chlorine, phosphorus, and the like, when added to lubricating oils and when subjected to high temperatures generated over limited areas by the pressure between moving parts, combine in some chemical manner with the metal of such parts to produce protective films of microscopic thickness which adhere tenaciously to the metal surfaces, and prevent metal to metal contact.

Lubricants of the general character referred to above may consist of blends of a petroleum oil with a saponiflable 011 containing as extreme pressure agents, either as free elements or as chemical compounds, sulfur, chlorine, phosphorus and the like. The added compounds are usually and preferably/somewhat inactive chemically at ordinary opefating temperatures, becoming more reactive with the metal surfaces, however, when such surfaces are subjected to the high temperatures which result from the frictional heat generated by the transmission of power through a gear train. In the past it has been necessary to compromise between extreme pressure additives which, on the one hand, are effective, when needed, to provide the type of protecting film mentioned above, but are objectionably corrosive over aperiod of time to metals such as copper and steel, and those which, on the other hand, are non-corrosive but are only moderately effective as extreme pressure agents.

Presumably, the microscopically thin protective films which are formed on metal surfaces in the manner referred to above consist of metal sulfides, chlorides, phosphides and the like. Thus, when sulfur, chlorine, phosphorus and like mate- 2 rials are used on steel gears (such as for example, hypoid gears in automobile driving axles), where unit pressures are very high at times, iron sulfides, chlorides, phosphides and the like are formed. Analogous compounds are formed with other metals.

Numerous compounds have been used in the past for the purposes described above. Among them are inorganic materials such as the phosphorus sulfides, for example, P483, elemental phosphorus, arsenic, selenium, lead compounds,

' oxides of phosphorus, various chlorides, etc. It

is well known for example, that phosphorus sulfldes may be dissolved in and/or reacted with various fatty bodies such as fatty-oils, fatty acids, sulfurized fatty oils, halogenated hydrocarbons and the like to impart E. P. characteristics thereto. Such compositions may then be used directly as extreme pressure lubricants or, more commonly, they are supplied as concentrated additives for use in small quantities in mineral 011 base lubricants.

It is also well known that organic phosphates, for example, tricresyl phosphate, may be used in fatty oils or acids or in mineral oil or mixtures thereof, either with or without other additives to impart certain desirable characteristics to lubricants. In particular, tricresyl phosphate has been found to have certain merit as an antioxidant and as an oiliness agent.

As suggested above, although the characteristics of the various materials heretofore used such as sulfur, phosphorus, chlorine and various compoundsthereof, are well recognized, the more effective extreme pressure compounds have objectionable corrosive tendencies. In many cases it has been necessary to limit the extreme pressure characteristics of a given compound to avoid corrosion of metals on which the lubricant is to be used. In other cases, it has sometimes been necessary to tolerate a limited though objectionable amount of corrosion in order'to obtain the necessary extreme pressure characteristics in a lubricant. For example, the addition of a relatively large amount of phosphorus sequisulflde, P483, to a fatty oil containing sulfur, has been found to give to lubricants very good extreme pressure characteristics, but the use of such relatively large quantities of the phosphorus sulfide has been' found also to make the lubricant seriously corrosive to metals. On the other hand, certain organic phosphates and phosphites have little corrosive tendency but also are not very effective as extreme pressure additives although moderately useful in smaller quantities for this purpose. An example of the latter is tricresyl phosphate. v

It is an object of our invention to enhance the extreme pressure characteristics of lubricants and additives of the aforesaid character while, at the same time, limiting or eliminating their cor rosivity. It is a further object of this invention to accomplish the foregoing by taking advantage of certain unexpected properties which we have discovered in the combination of phosphoruscontaining materials of inorganic and organic types, respectively.

Within certain limits we have found that the extreme pressure characteristics of a good lubricant, for example, a blend of a mineral oil and a fatty oil containing sulfur and phosphorus may be increased by increasing the total phosphorus content. We have found that materials such as tricresyl phosphate may be added to a lubricant containing an inorganic phosphorus compound, such as P483, for example. to increase total phosphorus content and improve extreme pressure characteristics, without increasing the corrosivity oi' the oil.

Up to a certain point. the degree to which the extreme pressure quality is imparted to an oil appears to be in more or less direct ratio to the increase in total phosphorus content, other things being equal. When inorganic phosphorus alone is used as an extreme pressure additive. a point is soon reached where the increa e in hosphorus content causes the lubricant to become objectionably corrosive, as indicated by excessive staining of copper and steel at elevated tem eratures. We have found, however. that when an or anic phos-. phate or phosphite is utilized to sup ly a part of the phosphorus content. the over-all phosphorus content of the lubricant may be brou ht to relatively high levels, with substantially the same beneficial load bearing characteristics, without exhibiting objectionable corrosive tendencies. In other words, the combination of an inorganic phosphorus compound, such as phosphorus sulfide, and an organic phosphorus containing material. such as tricresyl phosphate, or in general an aryl or alkyl phosphate. or phosphite, has the very desirable quality of imparting good extreme phosphorus containing additives effects a new and highly u eful result, making it possible to increase considerably the overall phosphorus content of the lubricant and thus improve its extreme pressure properties materially without pro-.

ducing severe corrosive effects, on the one hand. and without permit ing severe wear, such as would occur with lubricants 01' lower extreme pressure characteristics, on the other hand. As suggested above, such lubricants have special value in certain types of gearing, a particular application being found in heavy duty gearing such, for example, as the hypoid and other gearing used in truck axles. v

The lubricants contemplated by our invention may also contain other additives such as oxidation inhibitors, pour point depressors', and the like. They may contain various other organic or inorganic compounds, or free elements, including sulfur, chlorine, arsenic, selenium, tellurium, soaps, vegetable oils and/or other known ingredients. It will be understood that the various sulfides of phosphorus and various aryl and alkyl phosphates and phosphites are contemplated as being within the scope of our invention. While tricresyl phosphate has been mentioned above, the various esters of phosphoric and phosphorous acids may be used as the organic additive, and the substitution of the hydrogen atoms of phosphoric and phosphorous acids by alkyl or aryl radicals to form either complete or partial esters is contemplated.

' The following data illustrate the superior properties which we have observed on test of certain specimens of lubricating compounds made according to our invention. It will of course be understood that the scope of the invention is not limited to the'particular composition described hereinbelow.

One extreme pressure additive for lubricating oil, which is found to be highly satisfactory, consists of the following composition:

Per cent Sperm oil 89.9 Sulfur 5.8

- Phosphorus sesqui sulfide (P4Sa) I 0.5 Tricresyl phosphate 3.8

Several specific examples of compositions which were tested for extreme pressure characteristics and for corrosion are given:

EXAMPLE 1 1880 grams of natural winter sperm oil 45 and 120 grams of sulfur were stirred and heated in a beaker, raising the temperature to 385 F. and maintaining this temperature for 1 hours to permit complete reaction of the sulfur, followed by natural cooling to room temperature. The next day,'the sulfurized product was heated to 210 F. and 10 grams of phosphorus sesquisulfide (P483) was added and the temperature maintained for eight hours with constant and thorough stirring, followed by natural cooling.

A portion of this additive was blended with mineral oil, in the proportions of 10 parts of the additive to parts of mineral oil, to yield a lubricant meeting SAE 90 grade requirements. This was tested on the Timken machine and was sub jected to copper and steel staining tests. ond portion of additive was mixed with tricresyl phosphate in the proportions of 4 parts tricresyl phosphate to parts'of additive and the resulting product was blended with 896 parts of mineral oil and tested as before. The results of these tests are shown in Table I, below.

A see Table I Additives Oil Blends oi Additive 5 Timken Machine No. Per Cent Per Cent p P. TOP 1 0 Scar P S Test Load 2 Width 1 0 5 0. 0 33 1. 35 31, 300 P858. 1 0. 5 4. 0 51 1. 35 48, 400 Do. 2 0. 4 0. 0 43 l. 5 36, 700 D0. 2 0.4 4.0 51 l. 65 39. 600 D0. 3 0. 5 0. 0 43 1. 65 33, 400 D0. 3 0. 5 4. 0 51 I 1. 5 41, 100 Do.

I Tricresyl phosphate.

Pounds on lever arm.

I Unit=l-64 inch.

4 P. s. i.=pounds per square inch determined by total pressure measurement of scar widt etc.

1 hour at 250 F. (CRC-L-16-445 Procedure).

EXAMPLE 2 2117.5 grams of No. 1 lard oil, 125 grams of light mineral oil (45 S. S. U. at 210 F), 12.5 grams of sulfur monochloride, and 185 grams of sulfur were mixed and charged into an autoclave. The autoclave was then flushed with hydrogen sulfide, closed, and heated to 330-340" F. for 8 hours, maintaining a gauge pressure of approximately 7.5 lbs. of hydrogen sulfide, and

with continuous stirring throughout the reaction period. The sulfurized product was removed and cooled and subsequently was recharged together with 10 grams of phosphorus sesquisulfide. Hydrogen sulfide pressure of -7.5 lbs. gauge was maintained as before and heat applied to main tain a temperature of 220-230 F. for 5 hours. The product was removed and cooled.

parts of the above product and 90 parts of mineral oil were blended to meet the requirements of an SAE 90 lubricant and tested as before. 0.4 part of tricresyl phosphate was added to the blend and the tests were then repeated. As shown in Table I, the addition of tricresyl phosphate materially improved the load carryin properties of the lubricant without causing any increase in copper or steel staining.

An example of a large scale preparation is shown below:

EXAMPLE 3 16,600 grams of natural winter sperm oil 45 was placed in a glass-lined reactor equipped with a high-speed mixer and a loose-fitting cover and heated to 280 F. with agitation. 1059.6 grams of sulfur was added and heating continued, reaching 385 F. in approximately onehalf hour. The temperature was held at 385 F. 1: 5 F. for one and one-half hours and the mixture was then cooled by circulating water through a closed coil so that the temperature fell to 210 F. in 45 minutes. 88.7 grams of phosphorus sesquisulfide was then added and the temperature maintained at 210-21J5 F. for eight hours with agitation continuing. The product was then cooled.

Ten parts of the above product were then blended with 0.4 part of tricresyl phosphate and 89.6 parts of a mineral oil blend containing 0.5% of a pour point depressant in equal parts of a propane deasphalted and dewaxed mid-continent steam cylinder oil and an SAE grade phenol extracted mid-continent Table I. The composition of the finished lubricant is approximately as follows:

Per cent Sperm oil 9.35 Sulfur 0.60 P483 0.05 'Iricresyl-phosphate 0.40 S. A. E. 90 base lubricating oil 89.6

The SAE grade base gear 011 consists of:

Per cent Pour point depressor 1 0.22 Steam cylinder oil 44.58 S. A. E. 20 grade lubricating oil 44.78

Prepared by condensation of chlorinated paraifin wax with naphthalene.

Aside from the advantages mentioned above, we have discovered that synergistic improvements are obtained by the use of both an inorganic phosphorus compound-and an organic phosphorus compound, which cannot be obtained by the use of either type of material alone. To illustrate the synergistic improvements obtained, the following examples and data are given:

EXAMPLE 4 Natural winter sperm oil was treated with 12% of sulfur at 385 F. for 1 /2 hours after which one part of mineral oil (steam cylinder stock) was added to 4 parts of the hot sulfurized prodnot for quenching. The resulting product, containing about 9.5% sulfur, was subsequently treated with varying amounts of phosphorus sesquisulfide, the amounts being shown in Table lubricating II, by heating to 210-220 F. for eight hours.

The finished additives were then blended with the previously described SAE 90 grade mineral oil in the proportions of 10 parts of additive to 90 parts mineral oil by weight. In some cases tricresyl phosphate was added to the blends as shown.

It will be seen that a considerable improvement in load-carrying ability was obtained by the use of the two types of phosphorus compounds without imparting objectionable corrosive properties to the lubricant, with respect to either copper or steel. The load-carrying properties can be increased in a similar manner by the use of a larger amount of phosphorus sulfide but in this case the product is objectionably corrosive to both copper and steel. The addition of a similar amount of phosphorus in the form of an organic phosphate alone yielded a non-corrosive product, but the load-carrying ability was very stock. Test results on this blend are shown in poor.

Table II Additives Mineral Oil Blends Timken Machine Test Metal Corrosion Percent Percent Percent P TCP P Total OK Load Scar P. s 1 Steel Copper 0.0 0.0 0.0 43 12.0 4,600 No blackening Pass. 0.4 0.0 0.2 51 14.0 4, 660 o D0. 2.0 0.0 1.1 51 1.7 38,400 Blac Black. 0.0 8.0 0.7 43 14.0 3,940 No blackening. Pass. 0.4 5.0 0.6 51 1.7 ,400 do Do. 0.4 10.0 1.0 51 1.65 30,600 do Do. 0.4 33.3 2.9 51 1.9 33,800 d0 Do.

1 Pounds on lever arm.

inch.

' be employed in still higher concentrations.

The following is an" example of the use of alkyl phosphite.

Example A blend containing of an additive prepared as in Example 3 in 90% of mineral oil was tested with and without the addition of tributyl. phospite with the results shown below:

In obtaining the above data, a load rating of 51 was considered entirely satisfactory for the lubrication of truck hypoid gears, while lesser loads were considered unsatisfactory or at least doubtful. Tests on the Timken machine have been found to correlate quite well with actual service tests in such cases.

In practice, E. P. lubricants may be made by the addition to oils of various quantities of the additive composition shown in the first formula. This composition consists of 89.9% sperm oil with 5.8% sulfur and P48: and tricresyl phosphate added substantially in the quantities indicated, depending on the requirements. Satisfactory lubricants usually consist of mineral and/or fatty oil bases containing from 1 to of the concentrated E. P. additive. It will of course be understood that various oils, greases, fatty oils, fatty acids, etc. may be used as lubricants to which the organic and inorganic phosphorus compounds may be added in various quantities.

As another example, an extreme pressure oil or grease may comprise about 90% of an oil or grease base consisting of mineral, vegetable or animal oils, with or without soaps, and about 10% of a concentrated additive containing the extreme pressure compositions. The additive may comprise 85% to about 96% of a fatty body, such as a fatty oil or fatty acid, from 3% to 8% of sulfur (which is preferably cooked into the fatty body), from 0.1 to 1% of P483, and from 0.2 to 20% of tricresyl phosphate added (stirred in). Other compounds such as pour point depressants, oxida-- tion inhibitors, detergents, and the like, may be added as is well known in the art.

The additive itself may be manufactured and sold to the trade, to be incorporated in various quantities in mineral oils and other lubricants.- Depending on the properties required, the additive composition may be added to an oleaginous base in quantities as little as 2% or as great as 20%. For some special uses, the additive may Economic considerations, however, will generally limit use of the additive to the percentage ranges indicated.

summarizing the specific examples given above, the fatty material, e. g., sperm oil, lard oil, and the like, is first sulfurized by adding 3 to 12% by weight of sulfur, with or without sulfur chloride,

and cooking at a temperature of 330 to 400 F. for a vsuiiicient time to. substantially complete sulfurization. Thereafter, about 0.4 to 0.5% by weight of P483 is added and cooked for 5 to 8 hours at a temperature of about 210 to 230. F. The sulfurized and phosphorized fatty material is then combined with 1 to 10%, preferably about 4% of tricresyl phosphate and this additive is blended into mineral base lubricating oil in proportions of 1 to 20%, preferably about 10%.

5 Broader aspects of the invention have been indicated above.

While we have referred to the use of sperm oil and lard oil which we have found very satisfactory as a base for the additive, other animal and vegetable oils and the fatty acids relating thereto are contemplated. The fatty acids appear to be less suitable for truck gears but may be used for other purposes. Animal fats and oils are preferred. Also instead of or in addition to P483, other binary phosphorus compounds such as the other sulfides and the oxides "are suitable. Thus various inorganic phosphorus compounds may be added or substituted. Likewise, for tricresyl phosphate, such materials as triphenyl phosphates and other aryl phosphates and phosphites, or methyl, ethyl, or butyl phosphates and phosphites and analogous alkyl compounds, and various other organic compounds of the phosphorus acids and the like may besubstituted. The percentages of these materials used will vary, depending upon their compositions, solubilities, and general eifectiveness, but in general they will be used in quantities of from 0.1 to 20%, based on the finished lubricant. The inorganic materials mentioned above preferably will be used in quantities of from 0.1 to 2.0% in the additive or about 0.01 to 0.2% in the finished lubricant, depending on similar considerations. The percentages given throughout this specification refer to weight, based on the total additive or lubricant composition.

While we have described our invention in terms of specific ingredients and compositions, added in particular quantities, it will be understood that the invention is not limited thereto nor by any particular theories of reaction expressed herein. The compounds, com itions, and percentages may be varied considerably, as will be obvious to those skilled in the art. Such variations are within the purview of the invention, as limited only by the following claims.

We claim:

1. An extreme pressure lubricant consisting essentially of about to 99% of mineral base lubricating oil and 1 to 20% of an extreme pressure additive, said additive consisting of about 100 parts by weight of a sulfurized and phosphorized fatty material and about 4 parts of a composition selected from the group consisting of tricresyl phosphite and tricresyl phosphate, said sulfurized and phosphorized fatty material being prepared by first adding about 3 to 12% by weight of sulfur to said fatty material and heating the mixture to a temperature of about 330 to 400 F. for a sufficient time substantially to complete the reaction and thereafter reacting said sulfurized material with about 0.4 to 0.5% of P453 at a temperature of about 210 to 230 F. for about 5 to 8 hours.

2. Composition according to claim 1 wherein the proportions of oil and additive are about and 10%, respectively.

3. Composition according to claim 1 wherein to 12% by weight of sulfur to said fatty material and heating the mixture to a temperature of REFERENCES CITED ab t 330 to 400 F, for a sufficient ti b- The following references are of record in the stantially to complete the reaction and thereafter file of this Patent! reacting said sulfurized material with about 0.4 5 UNITED to 0.5% of P463 at a temperature of about 210 STATES PATENTS to 230 F. for about 5 to 8 hours. Number Name Date ELMER CYPHERS 2,285,853 Downing et a1. June 9, 1942 LOUIS OSBORNE, JR. 2,290,859 Burk et a1 July 28, 1942 10 2,346,356 Burk Apr. 11, 1944 2,382,121 Whittier Aug. 14, 1945 

1. AN EXTREME PRESSURE LUBRICANT CONSISTING ESSENTIALLY OF ABOUT 80 TO 99% OF MINERAL BASE LUBRICATING OIL AND 1 TO 20% OF AN EXTREME PRESSURE ADDITIVE, SAID ADDITIVE CONSISTING OF ABOUT 100 PARTS BY WEIGHT OF A SULFURIZED AND PHOSPHORIZED FATTY MATERIAL AND ABOUT 4 PARTS OF A COMPOSITION SELECTED FROM THE GROUP CONSISTING OF TRICRESYL PHOSPHITE AND TRICTESYL PHOSPHATE, AND SULFURIZED AND PHOSPHORIZED FATTY MATERIAL BEING PREPARED BY FIRST ADDING ABOUT 3 TO 12% BY WEIGHT OF SULFUR TO SAID FATTY MATERIAL AND HEATING THE MIXTURE TO A TEMPERATURE OF ABOUT 330* TO 400*F. FOR A SUFFICIENT TIME SUBSTANTIALLY TO COMPLETE THE REACTION AND THEREAFTER REACTING SAID SULFURIZED MATERIAL WITH ABOUT 0.4 TO 0.5% OF P4S3 AT A TEMPERATURE OF ABOUT 210* TO 230*F. FOR ABOUT 5 TO 8 HOURS. 